1. Field of the Invention
The present invention relates to a cutting tool, and a throw-away insert for the cutting tool. The throw-away insert is clamped securely to substantially a peak end of a holder of the cutting tool with a clamp screw.
2. Description of the Related Art
In a category of automatic lathes such as a cam-type automatic lathe, an NC (numerical control) automatic lathe and the like, there is included a machining equipment which is provided with a plurality of turrets. The turrets of the machining equipment mount cutting tools. The cutting tools are disposed radially when viewed in a direction along a rotational axis of a chucked workpiece (cut material).
More specifically, as is seen in FIG. 8, the machining equipment is provided with five turrets 1 to 5 which are disposed around a rotational axis of a workpiece W. When viewed in the direction along the rotational axis of the workpiece W, the five turrets 1 to 5 are disposed radially. Each of the turrets 1 to 5 clamps one of respective cutting tools 11 to 15. Each of the cutting tools 11 to 15 has a cutting blade whose peak end is distant from the workpiece W in a standby condition, namely, when a machining operation is not under way. On the other hand, when the machining operation is under way, the cutting tool (singular or plural in number) having the cutting blade for the machining operation is (are) conveyed in a direction perpendicular to the rotational axis of the workpiece W and toward a center of the rotational axis of the workpiece W. The workpiece W is cut with the thus conveyed cutting tool(s) in a predetermined manner. The cutting tool(s) is (are) so controlled as to return to the original point after the machining operation. With this, the cutting tool {singular or plural in number (plural cutting tools are conveyed simultaneously)} is (are) conveyed one after another for the required machining operation.
Of the above automatic lathes, the one for machining a shaft part (small diameter) such as those used for watch, clock, camera, instrument (meter), computer and the like uses a cutting tool that is of a type whose holder is brazed with an insert (formed with the cutting blade).
Use of the cutting tool having the above xe2x80x9cbrazed insertxe2x80x9d instead of a xe2x80x9cthrow-away insertxe2x80x9d is probably attributable to causes described in the following three paragraphs:
The cutting tools mounted on the turrets of the above automatic lathe are disposed radially on a flat surface which is perpendicular to the rotational axis of the workpiece W. Thereby, as is seen in FIG. 8, the smaller the workpiece W is in external diameter, the closer the peak ends (of the cutting tools) are to each other, both in the standby condition and when the machining operation is under way.
In terms of the cutting tool having the throw-away insert: The workpiece W having the external diameter not more than 15.0 mm is ordinarily not usable. This is attributable to an interference of the cutting tools (collision with each other) each of which has the throw-away insert clamped with a clamp screw (The interference is caused even though the cutting tool has a comparatively compact peak end.).
In terms of the cutting tool having the brazed insert: Contrary to the cutting tool having the throw-away insert, the cutting tool having the brazed insert can be subjected to a grinding (at the peak end of the cutting tool, including the brazed insert) so as to prevent the interference (collision), without causing failures such as decrease in locking strength of the brazed insert. With this, the cutting tool having the brazed insert is usable.
The brazed insert is, however, high in cost, involving increase in machining cost. Moreover, the cutting tool having the brazed insert is formed through the grinding, which is responsible for decrease in precision (and/or accuracy) of centering (in other words, adjusting position of the cutting blade) during replacement of the cutting tool having the brazed insert. This involves further preparation steps.
In view of the above feature of the cutting tool having the brazed insert, use of the cutting tool having the throw-away insert is preferred even in such applications as machining the shaft parts (small diameter) by means of the automatic lathe.
It is therefore an object of the present invention to provide a cutting tool having a throw-away insert, for machining a workpiece such as a shaft part defining a small external diameter.
More specifically, the cutting tool is plural in number each of which is mounted on one of a plurality of turrets disposed radially when viewed in a direction along a rotational axis of a chucked workpiece. The cutting tool (having the throw-away insert) is the one used for an automatic lathe such as a cam-type automatic lathe, an NC automatic lathe and the like.
According to a first aspect of the present invention, there is provided a cutting tool disposed on a turret. The cutting tool comprises: a holder having a peak end, and a throw-away insert clamped to the peak end of the holder with a clamp screw. The holder comprises: a bottom face and a peak end face defining a corner of the holder. The corner of the holder forms a chamfered face. The throw-away insert comprises: a bottom face and a relief face defining a corner of the throw-away insert. The corner of the throw-away insert forms a chamfered face.
According to a second aspect of the present invention, there is provided an automatic lathe for machining a round-rod workpiece (W) which is chucked on the automatic lathe and has an external diameter of not more than 5.0 mm before a machining operation. The automatic lathe comprises: a plurality of turrets (1, 2, 3, 4, 5) so disposed on the automatic lathe as to form a radiation when the plurality of the turrets (1, 2, 3, 4, 5) are viewed in a first direction along a rotational axis of the workpiece (W); and a plurality of cutting tools (101, 102, 103, 104, 105) disposed on the plurality of the turrets (1, 2, 3, 4, 5) in such a manner as to define a radial angular interval of 45xc2x0 between two of the adjacent cutting tools (101, 102, 103, 104, 105). Each of the cutting tools (101, 102, 103, 104, 105) comprises: a holder (111) having a peak end; and a throw-away insert (51, 52, 53, 54, 55) clamped to the peak end of the holder (111) with a clamp screw (130). The holder (111) comprises a bottom face (114) and a peak end face (138) defining a corner of the holder (111). The corner of the holder (111) forms a chamfered face (132) so as to prevent the cutting tools (101, 102, 103, 104, 105) adjacent to each other from causing an interference with each other when the cutting tools (101, 102, 103, 104, 105) are at least one of in a standby position and in the machining operation. The throw-away insert (51, 52, 53, 54, 55) comprises a bottom face (154) and a relief face (158) defining a corner of the throw-away insert (51, 52, 53, 54, 55). The corner of the throw-away insert (51, 52, 53, 54, 55) forms a chamfered face (152) so as to prevent the cutting tools (101, 102, 103, 104, 105) adjacent to each other from causing the interference with each other when the cutting tools (101, 102, 103, 104, 105) are at least one of in the standby position and in the machining operation.
Hereinafter described is TiCN coating as well as surface roughness of throw-away inserts.
According to the illustrated embodiment of the present invention, parent material (or base material) of the throw-away insert is extremely smooth having a surface roughness Ra (by JIS=Japanese Industrial Standard) not more than 0.3 xcexcm.
Herein, Ra is technically referred to as xe2x80x9ccenter-line mean roughness.xe2x80x9d The Ra is also referred to as xe2x80x9carithmetical mean roughnessxe2x80x9d which is one of surface roughnesses defined by JIS B 0601 (1994).
The surface of the parent material of the throw-away insert is coated with a thin TiCN layer not more than 2 xcexcm in thickness. Thereby, the surface (TiCN coat) of a blade end of the throw-away insert is small in irregularity. The thus formed blade end of the throw-away insert grows without causing great distortion, and therefore, is welded stably. As a result, even a free cutting steel is cut accurately and/or precisely (dimensional tolerance: xc2x10.01 mm), to thereby machine workpieces in large number.
Herein, the TICN coating layer (not more than 2 xcexcm) according to the illustrated embodiment of the present invention is thinner than conventional coating layer (for example, 3 xcexcm to 5 xcexcm). In spite of the thinness of the TiCN coating layer under the present invention, the cutting tool has a longevity. This longevity is attributable to the above stable welding of the blade end of the throw-away insert, and this stable welding is maintained preferably.
The parent material of the throw-away insert according to the illustrated embodiment of the present invention is made of various materials such as hard metal (or cemented carbide), ceramic, cermet (an acronym for ceramic metalxe2x80x94from Dictionary of Science and Technology issued by Academic Press), high speed steel and the like. The hard metal is, however, preferably the one whose raw material is made of ultra-fine-particle not more than 1 xcexcm in grain size (Hereinafter such hard metal is referred to as xe2x80x9cultra-fine-particle hard metal.xe2x80x9d). As compared with an ordinary hard metal, the ultra-fine-particle hard metal under the present invention is high in toughness and hardness, thereby featuring good blade standing (in other words, good machinability forming an acute blade end of the throw-away insert). Moreover, the ultra-fine-particle hard metal is excellent in wear resistance as well as failure resistance.
The center-line mean roughness Ra (not more than 0.3 xcexcm) according to the illustrated embodiment of the present invention is not a must for the entire surface of the parent material of the throw-away insert. In other words, xe2x80x9cnot more than 0.3 xcexcmxe2x80x9d should be applied to at least the blade end of the throw-away insert.
Moreover, according to the illustrated embodiment of the present invention, the TiCN coating layer may be single or multiple. To form the TiCN coating layer having thickness of not more than 2 xcexcm, shorter (than conventional method) vapor deposition time is preferred.
The above sums up description of the TiCN coating as well as the surface roughness.
The other objects and features of the present invention will become understood from the following description with reference to the accompanying drawings.